In vivo percutaneous absorption of capsaicin, nonivamide and sodium nonivamide acetate from ointment bases: Skin erythema test and non-invasive surface recovery technique in humans

Nonivamide (NVA) and sodium nonivamide acetate (SNA) are both synthetic analogues of capsaicin. In this present study, the in vivo skin erythema test and non-invasive surface recovery techniques were performed in humans for capsaicin, NVA and SNA after transdermal ointment application. In order to quantify the skin erythema and irritation caused by capsaicin and its analogues, laser Doppler flowmetry (LDF) was utilized for determining the cutaneous blood flow to assess the degree of irritant reaction. In the study of surface recovery technique, NVA hydrophilic ointment base showed higher flux and cumulative absorbed amount than the other formulations. In the study of skin erythema test, capsaicin caused severer skin irritation than NVA in humans. Moreover, there was no significant difference between the erythema levels of SNA and control group indicating that SNA produced no skin irritation or pungent sensation. In addition, increased skin temperatures were detected after transdermal application of capsaicin, NVA and SNA ointment bases. The trend of the skin temperature profiles was consistent with that of skin erythema test by laser Doppler flowmetry suggesting that increased skin temperatures may reflect the degree of vasodilation produced by irritation in the treated skin area. In the study of the skin erythema test using various concentration levels of capsaicin and NVA, the various doses from hydrophilic ointment did not markedly influence the pungent and irritant skin reactions after transdermal application.